1. Field of the Invention
This invention relates to an amplifier apparatus suitable for use in communication terminals such as mobile phones, base stations, and RF circuits.
2. Description of the Related Art
In the mobile communications terminals such as mobile phones, base stations, and RF circuits, a signal to be transmitted is amplified by an electric power amplifier before transmitted. At that time, an intermodulation distortion component is caused in an output of the amplifier. Since this intermodulation distortion component appears as noises in the signal transmitted, a feedback-type amplifier or any ordinary type of amplifier has been used in the conventional art to remove this intermodulation distortion component.
FIG. 18 of the accompanying shows a distortion feedback-type amplifier disclosed in Japanese Patent Laid-Open Publication No. HEI 5-167356. The distortion feedback-type amplifier 100 of FIG. 18 comprises a first dividing circuit 101, a first phase/power level regulating circuit 102, a first amplifier (primary amplifier) 103, a second dividing circuit 104, a second phase/power level regulating circuit 105, a first combining circuit 106, a second amplifier (auxiliary amplifier) 107, a band-pass filter 108a, a third phase/power level regulating circuit 108b, and a second combining circuit 109.
The first dividing circuit 101 divides an input signal from an input terminal (IN) to pick up a part of the input primary signal as an auxiliary signal for distortion detection (described later). The first phase/power level regulating circuit 102 regulates the phase and the power level of the auxiliary signal obtained by the first dividing circuit 101.
The primary amplifier 103 amplifies the primary signal received from the first dividing circuit 101, and the second dividing circuit 104 picks up a part of an output of the primary amplifier 103.
The second phase/power level regulating circuit 105 regulates the phase and the power level of the signal picked up by the second dividing circuit 104. The first combining circuit 106 combines the signal (frequency spectrum 114) from the second phase/power level regulating circuit 105 and the auxiliary signal (frequency spectrum 115) that has been regulated in phase/power level by the first phase/power level regulating circuit 102 to cancel a primary signal component contained in the output (frequency spectrum 113) from the primary amplifier 103 for detecting an intermodulation distortion component (hereinafter also called xe2x80x9cdistortion componentxe2x80x9d).
For this purpose, the first phase/power level regulating circuit 102 and the second phase/power level regulating circuit 105 regulates phase rotation and attenuation of the input signal in such a way that a primary signal component 130 in the amplified signal (frequency spectrum 114) is combined with the auxiliary signal (frequency spectrum 115) in opposite phases at the same power level by the first combining circuit 106.
The auxiliary amplifier 107 amplifies the distortion component (frequency spectrum 116) obtained by the first combining circuit 106. The third phase/power level regulating circuit 108b regulates the phase and power level of the output of the auxiliary amplifier 107. The band-pass filter 108a removes unnecessary band components in the signal from the third phase/power level regulating circuit 108b. 
Since the phase is rotated through 360 degrees between the opposite ends of the pass band in the band-pass filter 108a, a phase error with respect to a feedback signal (distortion compensating signal) is apt to be increased. Particularly, the wider the band width, the phase error would increase.
The second combining circuit 109 combines the distortion compensating signal (frequency spectrum 117) from the band-pass filter 108a with the primary signal (frequency spectrum 112) from the first dividing circuit 101 (frequency spectrum 118).
The third phase/power level regulating circuit 108b regulates the phase rotation and the power level of the distortion component obtained from the auxiliary amplifier 107 in such a way that the distortion component (frequency spectrum 116) amplified by the auxiliary amplifier 107 is opposite in phase to the primary signal component 130 of the signal (frequency spectrum 118) to be input to the primary amplifier 103 and that the distortion component 131 is canceled in the output (frequency spectrum 119) of the primary amplifier 103.
Namely, the second dividing circuit 104, the second phase/power level regulating circuit 105, the first combining circuit 106, the auxiliary amplifier 107, the third phase/power level regulating circuit 108b, and the band-pass filter 108a constitute a feedback loop (feedback system) 135 for an input/output system of the primary amplifier 103.
With this construction, in the conventional distortion feedback-type amplifier 100, the primary signal (frequency spectrum 111) input from the input terminal (IN) is divided into the primary signal (frequency spectrum 112) and the auxiliary signal (frequency spectrum 110) by the first dividing circuit 101, which auxiliary signal is then input to the first phase/power level regulating circuit 102 to be regulated in phase rotation and attenuation.
In the meantime, the primary signal (frequency spectrum 112) is amplified by the primary amplifier 103, at which time a distortion component 131 with respect to the primary signal component 130 is generated in the output (frequency spectrum 113) of the primary amplifier 103 due to the nonlinear characteristic of the primary amplifier 103.
Then a part of the output signal (frequency spectrum 113) of the primary amplifier 103 is picked up by the second dividing circuit 104 and is regulated in phase and power level by the second phase/power level regulating circuit 105.
The auxiliary signal (frequency spectrum 115) having passed the first phase/power level regulating circuit 102 is combined with the primary signal (frequency spectrum 114) in opposite phase at the same power level by the first combining circuit 106 to cancel the primary signal component 130, thereby extracting only the distortion component 131 (frequency spectrum 116).
The thus extracted distortion component 131 is amplified by the auxiliary amplifier 107 and is then regulated in phase rotation and attenuation by the third phase/power level regulating circuit 108b. After that, unnecessary band components other than the desired band, which are caused such as by oscillation in the feedback loop 135, are stopped by the band-pass filter 108a so that only the desired band component is output to the second combining circuit 109 as the distortion compensating signal (frequency spectrum 117).
The second combining circuit 109 thereby combines the distortion compensating signal (frequency spectrum 117) with the primary signal (frequency spectrum 112) to output the combined signal (frequency spectrum 118) to the primary amplifier 103.
As the result, the effect of the non-linear characteristic of the primary amplifier 103 is canceled in the signal(frequency spectrum 118) input to the primary amplifier 103. The resultant signal (frequency spectrum 119) whose intermodulation distortion component 131 is restrained is thus output from the primary amplifier 103 via the second dividing circuit 104, whereupon this signal is output from the output terminal (OUT) as the output of the distortion feedback-type amplifier 100.
Assuming that a transfer function of the distortion feedback-type amplifier 100 of FIG. 18 is obtained using an equivalent circuit of FIG. 19, the output eo of the distortion feedback-type amplifier 100 is given by
eo=Axc2x7eio+Dxe2x80x83xe2x80x83(1)
where ei is the primary signal to be input from the input terminal, D is the intermodulation distortion component to be added to the output of the primary amplifier 103, and A is the gain of the primary amplifier 103. In equation (1), eio is
eio=ei+(C+ei+Kxc2x7eo)xc2x7Bxc2x7Lxe2x80x83xe2x80x83(2)
therefore eo is
eo=A(1+Bxc2x7Cxc2x7L)/(1xe2x88x92Axc2x7Bxc2x7Kxc2x7L)xc2x7ei+D/(1xe2x88x92Axc2x7Bxc2x7Kxc2x7L)xe2x80x83xe2x80x83(3)
where K is the combining degree (attenuation rate) of the first combining circuit 106, B is the gain of the auxiliary amplifier 107, and L is the combining degree of the second combining circuit 109.
Here, as described above, because the auxiliary signal (frequency spectrum 115 of FIG. 18) is regulated so as to cancel the primary signal component contained in the primary signal (frequency spectrum 114) from the second phase/power level regulating circuit 105, Axc2x7K=xe2x88x92C. Therefore
eo=Axc2x7ei+D/(1+Bxc2x7Cxc2x7L)xe2x80x83xe2x80x83(4)
In this equation (4), the first term Axc2x7ei represents an amplitude component of the primary signal; the second term D/(1+Bxc2x7Cxc2x7L), an intermodulation distortion component. It turns out from this equation (4) that the intermodulation distortion component of the distortion feedback-type amplifier 100 of FIG. 18 depends upon B, C, L and also that the second term denominator, 1+Bxc2x7Cxc2x7L, should take a sufficiently large value in order to adequately remove the distortion component.
However, L, which is the combining degree of the second combining circuit 109, and C depending upon K, which is the combining degree of the first combining circuit 106, can be set to only an insufficiently large value with a limited range of variation.
Therefore, in order to diminish the intermodulation distortion component 131, the gain B of the auxiliary amplifier 107 must take an adequately great value. This, however, would not only cause increased power consumption of the whole circuitry but the circuit size and the number of components of the auxiliary amplifier 107 are also increased due to plural transistors needed, for example, thus consequently increasing the costs. And, because of a large output needed, the auxiliary amplifier 107 should be realized by an amplifier that generates no distortion. Also, a bad influence of phase rotation is also increased, affecting the regulations of phase rotation and power level in the third phase/power level regulating circuit 108b. Such construction is inadaptable in a wide range of band, and suppression of distortion in high rate signals cannot be attained.
With the foregoing problems in view, it is an object of the present invention to provide an amplifier apparatus that can effectively compensate for the distortion component contained in the output of an amplifier even in the presence of an auxiliary amplifier whose gain is small or even in the absence of such an auxiliary amplifier in a feedback system.
In order to attain the above object, according to the present invention, there is provided an amplifier apparatus comprising: an amplifier; a first dividing circuit, connected to an input side of the amplifier, for dividing an input signal into a primary signal, which is amplified by the amplifier, and an auxiliary signal, which is used for distortion detection; a distortion compensating signal generating circuit for generating a distortion compensating signal, which compensates a distortion component contained in an output of the amplifier, and inputting the distortion compensating signal to the amplifier; and a primary signal combining circuit (first combining circuit) for combining the primary signal obtained by the first dividing circuit with the distortion compensating signal, which is generated by the distortion compensating signal generating circuit.
With this amplifier apparatus of the present invention, since the distortion compensating signal obtained by the distortion compensating signal generating circuit is input directly to the amplifier while the primary signal to be amplified is added to the distortion compensating signal to combine these signals, a loss in the gain of the distortion compensating signal can be minimized, compared to a conventional amplifier apparatus in which the distortion compensating signal is added to the primary signal. This can eliminate the need for an amplifier (auxiliary amplifier) which amplifies the distortion compensating signal in the distortion compensating signal generating circuit, or can suppress at least the amplifying rate to a minimal necessary value, thus effectively compensating the distortion component as compared to the conventional technology.
Moreover, since the auxiliary amplifier can be unnecessitated, it is possible to reduce the power consumption, the circuit size, and the number of components of the amplifier apparatus, thus reducing costs.
As a preferred feature, (1) the first dividing circuit may be connected to an input side of the primary signal combining circuit so that the auxiliary signal can be obtained at an input side of the primary signal combining circuit with ease. As another preferred feature, (2) the first dividing circuit may be disposed between the primary signal combining circuit and the amplifier so that an auxiliary signal with a view to the influence of disturbance at the input side of the present amplifier apparatus can be obtained.
In the former case (1), since the value of distortion compensating signal obtained is large relatively to the primary signal, the distortion component generated in the amplifier can be removed more effectively.
In the latter case (2), since the auxiliary signal can be obtained with a view to the influence of disturbance occurred at the input side of the amplifier apparatus, it is possible to compensate the distortion component more effectively.
Particularly in this case, the first dividing circuit is the closer to the amplifier and the primary signal combining circuit is the closer to the input side, the more strongly the amplifier apparatus can prevent oscillation.
The present circuit is a feed-back circuit, which could generate oscillation. Precisely, if an oscillation component appears in the path starting from the primary amplifier, which passes through a coupler and an auxiliary amplifier and returns to the primary amplifier, oscillation could be caused in case of no means equipped for canceling the oscillation component. In the above-mentioned circuit, however, the oscillation component is input to the distortion compensating signal generating circuit, via the first dividing circuit, to be cancelled thereby on the basis of output of the primary amplifier including the same oscillation component. With this construction, signals in a range of band in which a distortion compensating process is available are free of the oscillation component generated in the feed-back circuit.
As still another preferred feature, the distortion compensating signal generating circuit includes: a second dividing circuit for picking up a part of the output of the amplifier; and a combining circuit (second combining circuit) for combining the part of the output of the amplifier, which part is picked up by the second dividing circuit, and the auxiliary signal obtained by the first dividing circuit in opposite phases to detect the distortion component; and a first phase/power level regulating circuit for regulating an output of the combining circuit in phase and power level to output the distortion compensating signal. This would guarantee an effective compensation for the distortion component with simple construction.
As a further preferred feature, the distortion compensating signal generating circuit further includes a differential amplifier to which a part of the output of the amplifier, which part is picked up by the second dividing circuit, and an auxiliary signal obtained by the first dividing circuit are to be input, and the combining circuit (second combining circuit) is constructed so as to combine outputs of the differential amplifier. With this construction, it is unnecessary to provide the combining circuit (second combining circuit), the amplifier for compensating the distortion of the signal extracted by the second dividing circuit and of the auxiliary signal, and the amplifier for amplifying the distortion compensating signal, as separate circuits. Since these circuits can be integrated onto a single microchip, it is possible to detect and amplify the distortion component with a simple construction.
As a still further preferred feature, the distortion compensating signal generating circuit includes an auxiliary signal combining circuit (third combining circuit) for combining a part of the auxiliary signal with the output of the combining circuit (second combining circuit). With this construction, since a primary signal component remaining in the output of the combining circuit (second combining circuit) can be removed, it is possible to improve the accuracy of detection of the distortion component so that a high-accuracy distortion compensating signal can be obtained, guaranteeing more effective compensation for the distortion component.
As an additional preferred feature, the distortion compensating signal generating circuit includes an amplifier-output combining circuit (fourth combining circuit) for combining part of the output of the amplifier, which part is picked up by the second dividing circuit, with the output of the combining circuit (second combining circuit). With this construction, since the primary signal component remaining in the output of the combining circuit (second combining circuit) can be removed, it is possible to improve the accuracy of detection of the distortion component so that a high-accuracy distortion compensating signal can be obtained, guaranteeing more effective compensation for the distortion component.
Further, a second phase/power level regulating circuit may be disposed between the second dividing circuit and the combining circuit (second combining circuit), and/or between the first dividing circuit and the combining circuit. The second phase/power level regulating circuit regulates the auxiliary signal and the part of the output of the amplifier, which is obtained by the second dividing circuit, in phase and power level, so that they have the same power level in opposite phase. With this construction, the auxiliary signal and the part of the output of the amplifier can be combined with ease by the combining circuit (second combining circuit) in the same power level as well as in opposite phase.
As another preferred feature, a primary signal attenuation compensating amplifier may be connected to an input side of the first dividing circuit. With this construction, since the primary signal attenuation compensating amplifier compensates for attenuation of the primary signal, which attenuation occurs when the primary signal combining circuit combines the primary signal with the distortion compensating signal, it is possible to obtain a sufficient gain of the primary signal so that a sufficiently large gain of the output of the amplifier apparatus and effective compensation for the distortion can be achieved.
As still another preferred feature, the distortion compensating signal generating circuit may include an auxiliary amplifier for amplifying the distortion compensating signal. With this construction, since the gain required for the distortion compensating signal can be secured by an amplifier having a minimal gain, it is possible to use even an amplifier with small power consumption in obtaining a high-accuracy distortion compensating signal, thus guaranteeing effective distortion compensation.
As a further preferred feature, the distortion compensating signal generating circuit includes a plurality of series-connected band-stop filters whose band-stop center frequencies are individually shifted off the band of the primary signal toward a low band side or a high band side to constitute a first composite filter which allows signal transmission in the band of the primary signal, or a low-pass filter and a high-pass filter which are connected in series to constitute a second composite filter which allows signal transmission in the band of the primary signal. With this construction, unnecessary components for the distortion compensating signal can be removed as unnecessary phase rotation in a pass band of the primary signal is prevented. Accordingly, it is possible to obtain an accurate distortion compensating signal so that more effective distortion compensation can be achieved.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.